New digital radio apparatus (digital mobile phones, for example) intended for operation in public data transmission networks are tested for type approval prior to being introduced into the market. Also newly manufactured units from a production line as well as repaired and/or serviced devices usually undergo certain testing. The equipment and methods used in the testing are usually defined in data transmission network standards. FIG. 1 illustrates a known test arrangement in which the apparatus to be tested is a mobile station (MS) 101 of a cellular radio system. The mobile station may also be called user equipment (UE). A simulation system (SS) 102 simulates a cellular radio system during the test. In this application such a system is called a simulation system or testing system. Testing the functioning of data transmission requires that an active data link 103 be setup between tie .SS and MS, which may be a radio link or a wire link through a testing interface at the mobile station.
Tests usually apply a technique in which a mobile station receives a downlink frame from the SS and sends back to the SS a corresponding uplink frame which contains an equivalent number of bits. The mobile station may even recycle to the SS the same individual bits that it received in the downlink direction, The SS examines whether the transmission or the operation of the mobile station caused errors in the flame. Arrow 104 depicts the loopback. The arrangement has been suitable for testing the mobile stations of known cellular radio systems since in the known systems the data transmission links are bidirectional and their capacity is distributed symmetrically: the capacities of uplink and downlink data transmission are equal. In mobile stations of new cellular radio systems, however, it is necessary to test functions that involve asymmetric distribution of data transmission capacity between uplink and downlink transmission. Moreover, mobile stations of new cellular radio systems may include functions based on unidirectional downlink data transmission the testing of which is naturally impossible using the method according to the prior art.
From an earlier Finnish patent application no. 981267 by the applicant, which is incorporated herein by reference, an alternative testing procedure is known which is suitable for the testing of data transmission arrangements with asymmetric capacities. In said procedure a mobile station selects from the bits of the downlink frame only a portion which is looped back to the uplink frames. The disadvantage of such an arrangement is that errors in those bits of the downlink frame that are not looped back uplink will remain undetected. In addition, this arrangement, too, is unsuitable for testing unidirectional downlink data transmission links.
Operators that are responsible for the operation of mobile phone networks and other cellular radio systems are extremely interested in the general quality of data transmission that the system can offer. Quality is an important factor in competition and often affects the decision-making when signing new subscriber contracts. The general quality of data transmission deals with factors such as the continuity of the coverage area (no dead spots nor areas with a very weak signal), the accessibility of channels (the network is not significantly jammed), as well as tolerance to several other simultaneous radio connections (simultaneous connections do not interfere with each other). A weak signal level and a high degree of interference cause bit errors in digital data transmission. The user notices the errors as difficulties in making and maintaining the connection, as well as in noise and interruptions therein. The technical reason for said symptoms is that the receiving apparatus must reject certain frames or protocol data units (PDUs), because they contain too many such incorrigible errors that cannot be accepted.
Known methods for measuring and optimising the general quality of data transmission require that a trained staff carries, within the system coverage area, particular measuring receivers, which produce location-bound measuring data of the various spots in the coverage area. In addition to the required personnel and equipment resources, another drawback of such arrangements is the fact that the data is rarely up to date. Both the operator of the system in question, as well as operators maintaining competing systems, continuously erect new base stations and adjust the transmission power of old base stations, which continuously changes the signal and interference conditions. The collecting and organising of the measurement data in a form that is suitable for practical network planning takes time and requires the setting up of special systems. In prior art telephone stations, it is possible to record statistical data as regards unsuccessfully established connections and quantities of established connections. In case of possible faults, there can also be recorded a fault code which roughly describes the nature of the disturbance. However, the fault statistic methods of the prior art are fairly approximate.